1. Field of the Invention
This invention relates to the field of foam forming equipment.
2. Description of the Prior Art
Fire-fighting nozzles for the application of a water stream or a water fog on a fire have been known for some time. Such nozzles are attached to a fire hose carrying a liquid stream, such as water, and frequently are adjustable to apply the fire-extinguishing liquid in a pattern ranging from a fog-like application to a straight stream, an example of which is made by Elkhart Brass Manufacturing Co., Inc. of Elkhart, Ind. However, an application of water is not desirable for all types of fires.
Fire-extinguishing foam-forming liquid compositions have been utilized in the extinguishing of certain types or classes of fires. Many of these foam-forming compositions will, when mixed with water and aerated with large quantities of air, form relatively stable foams, particularly for the extinguishing of large fires. Such liquid foam concentrates are known under the trademarks, Lightwater Brand.RTM., "AFFF/ATC" of Minnesota Mining and Manufacturing Company, Minnesota and "Emulsiflame.RTM." of Elkhart Brass Manufacturing Co., Inc. Other such foams are generally described in U.S. Pat. Nos. 3,772,195; 3,562,156; 3,578,590; and 3,548,949.
The foam-forming liquid compound has been generally supplied as a concentrate which was inducted into the flowing liquid stream by an in-line or by-pass foam eductor. The separate eductor was connected between the nozzle and the liquid stream pump or source. The foam concentrate was withdrawn by the eductor or pumped from the concentrate was withdrawn by the eductor or pumped from the concentrate storage and was then diluted and/or mixed with the liquid stream in the desired concentration. Thereafter, the foam-forming concentrate and liquid mix was aerated in a separate system, forming the foam which discharged from a nozzle.
Generally the foam applying nozzle used with the separate eductor has been of the same type utilized to apply water. Some water nozzles have had the stem-portion modified (the stem limits and assists in directing the water flow) for the application of the foam. These are non-aspirating peripheral jet nozzles.
Using such prior art concept and equipment, wherein the foam concentrate was first separately mixed with water and then the foam was generated by air aspiration and discharged through a nozzle, the distance the foam could be projected from the nozzle has been considerably shorter than the distance water alone could be projected through the nozzle. For example, with foam, the maximum distance was usually only about 170 feet whereas with water it was about 300 feet. The separate foam eductor limits the flow (gallonage per minute) and the line pressure to the nozzle. Typically, foam eductors handled between 30 and 250 gallons per minute; whereas, nozzles handled in excess of 1000 gallons per minute. The separate eductor constricted the complete flow of water creating a pressure drop of 30-40% across the eductor. This loss of pressure was created by the flow into the eductor working against backpressure due to the constriction. Thus, the previous separate foam eductor and nozzle limited the flow and range capabilities of the nozzle and required the firefighter to approach the fire more closely.
The discharge distance of foam has previously been increased using a balanced pressure proportioning system. This system included a pump, control valve and ratio flow controller (venturi) which introduced the foam concentrate under pressure into the hose behind the nozzle. Since this system was pressurized, the drop in pressure created by the separate eductor was reduced, which allowed the greater flow pressure to form at the nozzle. The balanced pressure proportioning system was rather cumbersome, required a power source for the pump, and was more expensive than the separate eductor and nozzle system.
Prior art in-line systems included what is known in the art as bladder tanks or pressure tanks. These are large tanks which have one compartment containing the concentrated foam-making solution and the second portion for holding water. The two portions were separated by a bladder or the water and foam concentrate commingled to some degree. The water portion was attached to a water intake line which always contained line pressure, but when needed for fighting a fire, water was introduced to the tank to increase the water pressure into the tank containing the foam solution plus the water. These prior art devices relied on a ratio flow controller (venturi) to mix the foam making concentrate and the water to make foam. This process resulted in essentially the same system as a balanced pressure system. The bladder tank replaced the pump used in the balanced pressure system. An additional disadvantage of the prior art systems was that using the pressure tank for mixing caused a significant time loss in replenishing the foam concentrate. The apparatus of the present invention results in a higher quality foam which signficantly increases the 25% drain time of the foam when applied in the tank. 25% drain time is defined as the amount of time 25% of the bubbles comprising the foam burst and form water, thereby losing some of the fire fighting blanketing capability.